Losing PPP when send SMS with CMUX | Telit Cinterion IoT Developer Community
February 26, 2020 - 4:09pm, 1751 views
I am talking to a PLS62-W over the UART interface at 921600 bits/s.
I can set up a PPP interface and it seems reliable. But I would like to receive and send SMS at the same time. The way forward seem to be to use CMUX mode, and the PPP link seems reliable on a MUX channel.
But often when I then send an SMS on another MUX channel, shortly afterwards I get a Modem Status Command on the MUX control channel saying that the PPP-channel's V24 octet has changed to 0x06 (FC asserted, CTS dropped). Shortly afterwards it returns to 0x0c (FC negated; DSR and CTS set).
Then I get a UIH message on the PPP channel that my PPP stack interprets as "LCP Terminated by Peer". And the PPP link is dropped. I observe that the TX activity pin stays low from here on (and I find it difficult to reset the PLS62 to restore normal operation).
What information should I capture to help identify whether this is a bug in my code, something in the PLS62 module, or something in the network? I should point out that the SMS itself does get through as intended, but it seems a coincidence that I lose PPP by sending a text.
I expect many most people who want to keep a PPP link up at the same time as sending an SMS do so over the USB interface. That is not an option for me.
I've just tried the same code with a Telit LE910EUv2 a few ***** without failure.
That's not proof that the problem lies with the PLS62-W because that did work for me a few *****; it just failed more often than it worked.
My PLS62-W gives "REVISION 02.000" in response to AT+CGMR
Hello,
Can I ask a few more questions? How frequently does it happen? Is hardware flow control configured on both sides and all lines connected?
As I undeerstand you have configured the fixed baudrate on the UART interface before starting the multiplexer.
As for USB there's also the second UART interface available that could be used instead.
Thanks,
Bartłomiej
Mea Culpa! It is possible that this was caused by a faulty antenna lead. I re-soldered a joint on this and have not had a problem since.
It happened most ***** I sent an SMS from the PLS62-W (which I do in response to an incoming SMS, after deleting all read SMS messages).
Yes I set the baud rate prior to starting CMUX. Hardware flow control is enabled in both directions. Initially I had a big circular buffer to DMA in each direction, but that does not allow fast response to incoming CMUX flow-control messages. So now on transmission I only DMA one CMUX packet at a time and check the reception buffer for flow-control mesages prior to sending the next one.
Thanks for your attention. I'll post if the problem returns.
Danish
OK, thaks for the update.